The present invention relates to a tire deflation warning device for use particularly with a tubeless tire for indicating and warning of a reduction of the internal pressure in the tubeless tire of a motor vehicle.
It has generally been recognized that it is highly important in terms of the traffic safety to detect an abnormal reduction of tire pressure and to warn an automobile driver of that effect. In view of this, various detecting and/or warning devices have heretofore been proposed. For example, one prior art detecting device utilizes a leaf spring deformable in proportion to the reduction of the tire pressure. However, this prior art device, although effective to provide an indication of the volume of the tire pressure reduced or remaining in terms of the magnitude of deformation of the leaf spring, has been found often to operate erroneously because physical properties of the leaf spring tend to be adversely affected by aging, the change in temperature and/or shocks and vibrations transmitted thereto from the wheels.
Of the prior art warning devices so designed as to have a capability of providing an indication of the tire pressure reduction to an automobile driver occupying a driver's seat inside the vehicle, mechanical, electromagnetic and radio warning devices are now well known. An example of the mechanical warning devices is disclosed in any one of the U.S. Pat. No. 3,265,822, patented Aug. 9, 1966, and the Japanese Patent Publication No. 55-127213 published Oct. 1, 1980.
The warning device disclosed in the U.S. patent comprises an actuating rod connected by a universally deflectable coil spring to a mechanical switch assembly which is demountably clamped to a wheel axle in a manner with the actuating rod extending downwards from the wheel axel towards the road surface. This device is so designed that, when the tire becomes deflated or overloaded, the free end of the actuating rod is upwardly deflected in contact with the road surface to switch on the switch assembly. This switch assembly is described as electrically connected to a warning light located for the attention of the driver.
The device of the U.S. patent referred to above has a disadvantage in that the driver will often be misled to the occurrence of the tire deflation when the free end of the actuating rod, positioned laterally spaced from the tire, contacts a discrete or continuous projection protruding upwardly from the road surface while the tire runs on a plain area of the road surface.
The warning device disclosed in the Japanese patent publication is complicated and delicate in design and operation and requires an air gauge or diaphragm valve to be fluid-connected to an air supply and removal valve, which air gauge is operatively coupled through an actuating wire to a switch assembly rigidly secured to a rim flange of a wheel on one side opposite to a corresponding bead portion of the tire. The switch assembly is described as electrically connected to a combination of a warning lamp and a buzzer.
Both of these prior art mechanical warning devices have a common disadvantage in that the reliability and the durability tend to be adversely affected by the accumulation of foreign matter such as dust and mud.
On the other hand, the prior art electromagnetic and radio warning devices have a disadvantage in that they tend not only to be adversely affected by an external magnetic field, but also to pose some problem associated with wave interference.